package pcsr.drivers.nxtDriver;

import java.lang.reflect.Array;

/**
 * Collected methods which allow easy implementation of <code>hashCode</code>.
 * 
 * Example use case:
 * <pre>
 * public int hashCode(){
 * int result = HashCodeUtil.SEED;
 * collect the contributions of various fields
 * result = HashCodeUtil.hash(result, fPrimitive);
 * result = HashCodeUtil.hash(result, fObject);
 * result = HashCodeUtil.hash(result, fArray);
 * return result;
 * }
 * </pre>
 */
public final class HashCodeUtil {

  /**
	 * An initial value for a <code>hashCode</code>, to which is added contributions
	 * from fields. Using a non-zero value decreases collisons of <code>hashCode</code>
	 * values.
	 */
	public static final int SEED = 23;

  /**
	 * booleans.
	 */
	public static int hash( int aSeed, boolean aBoolean ) {
    System.out.println("boolean...");
    return firstTerm( aSeed ) + ( aBoolean ? 1 : 0 );
  }

  /**
	 * chars.
	 */
	public static int hash( int aSeed, char aChar ) {
    System.out.println("char...");
    return firstTerm( aSeed ) + (int)aChar;
  }

  /**
	 * ints.
	 */
	public static int hash( int aSeed, int aInt ) {
    /*
    * Implementation Note
    * Note that byte and short are handled by this method, through
    * implicit conversion.
    */
    System.out.println("int...");
    return firstTerm( aSeed ) + aInt;
  }

  /**
	 * longs.
	 */
	public static int hash( int aSeed, long aLong ) {
    System.out.println("long...");
    return firstTerm(aSeed)  + (int)( aLong ^ (aLong >>> 32) );
  }

  /**
	 * floats.
	 */
	public static int hash( int aSeed, float aFloat ) {
    return hash( aSeed, Float.floatToIntBits(aFloat) );
  }

  /**
	 * doubles.
	 */
	public static int hash( int aSeed, double aDouble ) {
    return hash( aSeed, Double.doubleToLongBits(aDouble) );
  }

  /**
	 * <code>aObject</code> is a possibly-null object field, and possibly an array.
	 * 
	 * If <code>aObject</code> is an array, then each element may be a primitive
	 * or a possibly-null object.
	 */
	public static int hash( int aSeed, Object aObject ) {
    int result = aSeed;
    if ( aObject == null) {
      result = hash(result, 0);
    }
    else if ( ! isArray(aObject) ) {
      result = hash(result, aObject.hashCode());
    }
    else {
      int length = Array.getLength(aObject);
      for ( int idx = 0; idx < length; ++idx ) {
        Object item = Array.get(aObject, idx);
        //recursive call!
        result = hash(result, item);
      }
    }
    return result;
  }


  /// PRIVATE ///
  private static final int fODD_PRIME_NUMBER = 37;

  private static int firstTerm( int aSeed ){
    return fODD_PRIME_NUMBER * aSeed;
  }

  private static boolean isArray( Object aObject ){
    return aObject.getClass().isArray();
  }
}
